The sample size is calculated to detect at baseline at least 100 nasopharyngeal swab specimens positive for Streptococcus pneumoniae, and possibly further 100 positive swabs at both 6 and 12 months after recruitment. A probability sample of at least 1,300 children will be recruited. Children will be selected using a randomization list of assisted children less than 5 years-old that will be computer generated for any of participant Family Pediatrician, based on the Lombardy Regional Health Databases and using the National Insurance Number.